The present invention relates generally to the fields of protective relaying and test apparatus. More particularly, the invention relates, but is not limited to, a relay test set that utilizes a computer controlled voltage power supply to simulate secondary voltages and currents for testing a low voltage trip relay.
A problem addressed by the present invention is that most relay test sets having the ability to inject a minimum of ten amps of alternating current at fifty volts are large and expensive. These large and expensive test sets also use separate supplies for the current and voltage. The present invention incorporates the ability to inject both high current and voltage into the secondary inputs of a protective relay using a single computer controlled voltage power supply. By using this design, the relay test set is made to be both cost effective and portable. The secondary inputs of protective relays are used to connect the metering current and voltage transformers. By injecting the voltage and current into these inputs, the test set becomes a simulator of both current and voltage transformers.
To reduce both size and cost, such a test set requires a very efficient power supply that does not dissipate large amounts of heat. A unique aspect of the present invention is the use of a microcomputer module to control a variable voltage Class D power supply to vary both voltage and current as needed for the required test. The microcomputer also monitors the voltage and current being injected into the unit under test, UUT, to insure the proper levels are attained.
The present invention accomplishes several tasks in the area of protective relay testing. Typical relay test sets are large, heavy and costly. To reduce the size and weight of the test set, a small, highly efficient voltage and current source has been designed. Linear power supplies are very inefficient and require large heat sinks to dissipate heat. A presently preferred implementation of this invention incorporates a Class D switching amplifier design that greatly reduces the size of the power source needed to inject the correct voltage and current into the secondary inputs of a protective relay. To further reduce the size, weight and cost of the relay test set, one may also use a single voltage amplifier to drive both voltage and current secondary inputs of a protective relay, rather than using a separate voltage and current source. In so doing, this test set then becomes both a voltage transformer and current transformer simulator utilizing a single voltage power source at reduced size, weight and cost.
It is desirable for the power source to be variable while maintaining accuracy. To accomplish these goals, a microcomputer module may be incorporated to monitor both current and voltage being injected into a protective relay. This microcomputer may also automatically run the required relay tests and route the voltage or current to the appropriate inputs of the protective relay by direct control of a relay matrix.
Other features of the present invention are disclosed below.